1. Field of the Invention
The present invention relates generally to a laser device and particularly to a group-III nitride semiconductor laser device.
2. Description of the Related Art
In order to achieve an operation as a laser, an optical laser cavity comprising a pair of reflecting mirrors is required. In semiconductor laser devices (Fabry-Perot type) using such semiconductor crystal materials as GaAs, a multi-layer body including a laser structure is cleaved simultaneously with a GaAs crystal substrate and then this cleaved facet is used as a cavity mirror of the laser device.
As concerns a semiconductor laser device formed from group-III nitrides, sapphire is commonly used as the substrate. Since sapphire does not have a clear cleavage plane, the cavity mirror can hardly be formed by cleaving. Accordingly, the cavity mirror of the semiconductor laser devices is formed by dry etching such as reactive ion etching (RIE).
Sapphire is chemically very stable and is therefore etched little, so that a sapphire substrate 101 is left unetched after the dry etching process. As a result a terraced structure (a terrace portion 103) is formed as extending beyond a cavity mirror 102′ of a multi-layer body 102 formed from group-III nitrides, as shown in FIG. 1. In such a case, a part of a laser light 104 is reflected by the terrace portion 103, thereby a far-field pattern is formed as a plurality of spots in stead of a single spot. Thus, the semiconductor laser device 100 could not be used particularly as a light source for a optical storage device.
To overcome this problem, a method for transferring the multi-layer body on to a substrate which is highly cleavable and cleaving this sample to form the cavity mirror has been proposed. Specifically, the multi-layer body is formed on the sapphire substrate, and this sample is bonded onto a carrier substrate which is highly cleavable. After removing the sapphire substrate from the multi-layer body, the multi-layer body is cleaved along with the carrier substrate, thereby obtaining a laser device with a cleaved facet serving as the cavity mirror.